1. Field of the Invention
This invention relates to a reciprocating balance weight mechanism for a piston type internal combustion engine in which one or more reciprocating balance weights are driven according to the motion of a rotating cam.
2. Disclosure Information
In certain types of engines, it is very difficult to completely dynamically balance all of the moving masses therein. In engines of this nature the primary forces and couples may not be compensated for by means of counterbalancing weights on the rotating crankshaft. Secondary unbalances produced in the engine have frequently been treated through the use of balance shafts provided in the engine. These balance shafts incorporate eccentric weights which are rotated along with the shaft at typically twice the speed of the engine's crank shaft to produce a rotating couple or force for counter balancing the disturbing couple. Such balance shafts typically comprise a solid bar that is disposed adjacent the camshaft of crankshaft with a pair of eccentric weights mounted on the opposite ends of the bar. The weights project from the bar and are rotationally displaced 180.degree. from each other.
Although rotation of such a balance shaft has been found effective for balancing a rotating couple, the rotation of the eccentrically disposed weights produces bending of the solid shaft. This bending will result in radial deflections of the shaft which may be of considerable dimension, particularly at higher speeds. These deflections will cause the shaft to be bent into a somewhat S shape. This will result in the shaft moving from the desired axial alignment with the bearing supporting the shaft, thus imposing excessive loads on the bearings. These loads may cause excessive bearing wear and premature bearing failure. In addition, if the shaft is driven by a gear mounted on the shaft, the bending of the shaft will cause the gear to be deflected out of its proper plane of rotation. Thus, the gears will not be properly aligned and will not mesh properly. These factors will not only cause excessive wear but will also require more power to drive the shaft. Examples of balance shafts having the foregoing shortcomings are disclosed in the following U.S. Pats. Nos. 2,632,340; 2,838,957; 4,305,352; 4,508,069; and 4,523,553.
All of the previously known arrangements for balance shafts of the type thus far described suffer from yet another deficiency inasmuch as the multiple bearings required to properly suspend the shaft within the engine all consume engine power which would otherwise be available at the flywheel. This problem is further exacerbated by the fact that such balance shafts are commonly driven at twice the crankshaft speed which causes greatly increased frictional losses arising from shearing of the engine's lubricant at the bearing interfaces.
U.S. Pat. No. 1,958,148 discloses a device for counterbalancing or diminishing vibration occurring in stationary engine plants, in which a large mass block is elastically supported so that when excited by a cam operated lever means, the mass block and its spring mounting comprise a tuned absorber which will vibrate at a natural frequency determined by its own mass and the spring constant of the elastic mounting arrangement. Accordingly, the engine serves merely to excite the mass-spring system. This type of system is not suitable for operation at more than a small frequency range, and this would impose severe limitations on the available frequency response of such a system. In other words, the system of U.S. Pat. No. 1,958,148 would not be suitable to produce of damping needed with modern automotive engines, which operate at wide speed ranges.
It is an object of the present invention to provide a reciprocating balance weight mechanism for a piston type internal combustion engine which has reduced friction loss characteristics and no rotating bearings.
It is a further object of the present invention to provide a reciprocating balance weight mechanism having small packaging dimensions.
It is a further object of the present invention to provide a reciprocating balance weight mechanism which may be used to counteract both shaking forces and rocking couples of first, second and higher order harmonics all at once.